STRATIGRAPHY, STRUCTURE AND METAMORPHISM OF THE ESPLANADE RANGE, SOUTHEASTERN CANADIAN CORDILLERA

The Esplanade Syncline is part of a fold train (anticline-syncline-anticline) just east of the Selkirk Fan Axis, north of Rogers Pass (SE British Columbia). The fold train deforms strata of the Neoproterozoic Kaza Group and underlying units of the Mica Creek succession. The Lower Cambrian Hamill Group overlies these rocks in a syncline along the Fan Axis.The axial surface of the Esplanade Syncline dips southwest. Its vertical to overturned west limb is truncated by the Esplanade Thrust such that the west limb of the syncline is progressively eliminated southward toward Rogers Pass. The thrust repeats a panel of west-dipping strata over the west-dipping east limb of the syncline. The syncline is part of a fold propagation fold pair related to the thrust, and, in part, predates the thrust. The Rogers Pass region lies at the southern limit of the 400 km long Selkirk-Monashee-Cariboo (SMC) metamorphic complex, bounded on the east side by the garnet isograd. The garnet and staurolite isograds outline metamorphic highs and lows with the metamorphic synform roughly coinciding with the Esplanade Syncline. The metamorphic antiforms and synforms continue soutward to where the strata form a thrust-repeated homocline. The isograd pattern can therefore not be explained by folding of the isograds. The critical index minerals form porphyroblasts superimposed on the deformation fabric suggesting that metamorphism was syntectonic with the peak reached late in the deformation. Pressure-temperature pseudosections with coexisting staurolite and kyanite suggest pressures of about 6 kbar. The fold train described above and the narrow southern continuation of the SMC are truncated by the mid-Cretaceous (~100 Ma) Battle Range pluton suggesting tht the deformation and metamorphism are older than the mid-Cretaceous. The available geochronologic results are consistent with this interpretation. The metamorphic and deformation style suggest that the Esplanade Syncline formed in the deeper part of an Early Cretaceous suprastructure in the transition to the infrastructure.